1. Field of the Invention
The present invention relates to an OHC engine in which a valve operation system is housed in a valve operation chamber formed between a cylinder head and a head cover joined to the cylinder head. The valve operation system includes a valve-operating cam that is rotatably supported by the cylinder head and is cooperatively connected to an intake valve and an exhaust valve; and timing transmitting means disposed between the valve operation system and a crankshaft. The timing transmitting means includes a driven wheel that rotates together with the valve-operating cam and a transmission belt that is wrapped around the driven wheel, so that oil within a crankcase is carried by the transmission belt and is supplied to the valve operation chamber. In particular, it relates to an improvement of a lubrication structure for the valve operation system.
2. Description of the Prior Art
A conventional lubrication structure for an OHC engine is already known in, for example, Japanese Patent Application Laid-open No. 8-177441, wherein oil is supplied to a valve operation system by means of the oil being carried by a timing belt that is for transmitting the rotational power of a crankshaft to the valve operation system.
In order to lubricate a valve operation system with the oil supplied to a valve operation chamber by means of a timing belt, etc., it is necessary to splash the oil within the valve operation chamber. In the above-mentioned conventional arrangement, the oil is splashed by means of inertial force and centrifugal force imposed on the oil in the section where the timing belt is wrapped around a driven pulley, but in order to satisfy the lubrication requirements that become more strict as the load and rotational speed of an engine increase, it is necessary to splash the oil more finely.
In a lubrication structure disclosed in Japanese Patent Application Laid-open No. 9-151720, a wall is provided on a head cover, in a section where a timing belt is wrapped around a driven pulley, at a position on a line that extends over the slack side of the timing belt, the oil that has separated from the timing belt due to inertial force collides with the wall, and the oil is thereby atomized so as to fill a valve operation chamber.
Even in accordance with the lubrication structure of Japanese Patent Application Laid-open No. 9-151720, it is difficult to splash the oil uniformly within the valve operation chamber, and there is a possibility that, among the members forming the valve operation system, oil supply to the member that is positioned on the tensioned side of the timing belt might become insufficient.
The present invention has been carried out in view of the above-mentioned circumstances, and it is an object of the present invention to provide a lubrication structure in an OHC engine that can supply oil uniformly to each section of a valve operation system.
In order to accomplish this object, in accordance with a first aspect of the present invention, there is proposed a lubrication structure in an OHC engine. The lubrication structure includes a valve operation system housed in a valve operation chamber formed between a cylinder head and a head cover joined to the cylinder head, the valve operation system including a valve-operating cam that is rotatably supported by the cylinder head and is cooperatively connected to an intake valve and an exhaust valve. The lubrication structure also includes timing transmitting means disposed between the valve operation system and a crankshaft, the timing transmitting means including a driven wheel that rotates together with the valve-operating cam and a transmission belt that is wrapped around the driven wheel, so that oil within a crankcase can be carried by the transmission belt and be supplied to the valve operation chamber. The head cover is provided with an arc-form curved cover part for covering the upper part of the driven wheel, and the curved cover part above the driven wheel is provided integrally with a plurality of oil splashing ribs that are placed at intervals along the rotational direction of the driven wheel to project toward the side that is closer to the transmission belt.
In accordance with the above-mentioned arrangement, the oil that has been conveyed to the valve operation chamber while attached to the transmission belt is made to separate from the transmission belt due to centrifugal force in the section where the transmission belt is wrapped around the driven wheel, and the oil so detached collides with the oil splashing ribs and is atomized. Since the oil splashing ribs are provided on the curved cover part of the head cover at a plurality of positions at intervals along the rotational direction of the driven wheel, when the transmission belt runs in the section where it is wrapped around the driven wheel, the oil that has passed by one oil splashing rib collides with a following oil splashing rib and is splashed, thereby reliably splashing the oil at a plurality of positions and ensuring that the oil can reliably reach each part of the valve operation system. Moreover, the plurality of oil splashing ribs also have the function of reinforcing the head cover.
Furthermore, in accordance with a second aspect of the present invention, there is proposed a lubrication system in an OHC engine, wherein the valve operation system further includes intake side and exhaust side rocker arms cooperatively connected to the corresponding intake valve and exhaust valve and individually in sliding contact with the lower part of the valve-operating cam at positions on opposite sides of, and an equal distance from, a vertical line passing through the rotational axis of the valve-operating cam coaxially and integrally formed with the driven wheel. A pair of the oil splashing ribs are placed outside a pair of vertical lines, in a projection on a vertical plane that is orthogonal to the rotational axis of the valve-operating cam, that pass through the parts of the rocker arms that are in sliding contact with the valve-operating cam. In accordance with the arrangement, the oil that has collided with the pair of oil splashing ribs can reliably reach the sections where the intake side and exhaust side rocker arms slide on the valve-operating cam. Reliable lubrication of the valve operation system can thereby be carried out by means of a small number of oil splashing ribs.
Furthermore, in accordance with a third aspect of the present invention, there is proposed an OHC engine wherein each of the oil splashing ribs is provided integrally with the curved cover part extending in a direction orthogonal to the rotational direction of the driven wheel. In accordance with the above-mentioned arrangement, the oil can collide with the oil splashing ribs at right angles, and the oil can thereby be splashed more finely.